The goal of the proposed research is to study how the human cognitive system responds to changing environments and behavioral goals rapidly and with great flexibility. The research combines collection of behavioral data and modeling of this data within Logan's Executive Control Theory of Visual Attention (ECTVA). The proposed experiments will use task switching methodology where two or more simple cognitive tasks (e.g. categorization or location of visual stimuli) are presented in close temporal order. Response time and accuracy measures provide information about the time course of processes involved in switching between tasks. Mathematical modeling of the behavioral data in ECTVA allows for the development of a formal model of executive control in task switching. Specific lines of experimentation will included 1) investigation of task similarity effects on task switching, 2) comparison of task switches that involve adding or deleting task components, and 3) examination of sequential versus simultaneous task presentation.